Dry-scrubbing media compositions and methods of production and use

ABSTRACT

Dry-scrubbing media compositions, methods of preparation and methods of use are provided. The compositions contain activated alumina and magnesium oxide. Optionally, activated carbon and other impregnates, such as hydroxides of group 1A metals, are included. The compositions exhibit improved efficiency and capacity for the removal of compounds, such as hydrogen sulfide, from an air-stream. The compositions are particularly useful for reducing or preventing the release of toxic gaseous compounds from the areas such as landfills, petroleum storage areas, refineries, drinking water systems, sewage treatment facilities, swimming pools, hospital morgues, animal rooms, and pulp and paper production sites.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/039,215, filed Mar. 25, 2008, which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The application relates to compositions and methods for the removal oftoxic, corrosive, harmful or malodorous compounds from an air-stream andmore particularly relates to the use of a dry-scrubbing media.

BACKGROUND OF THE INVENTION

Undesirable airborne compounds, including chlorine and sulfur containingcompounds, hydrogen sulfide, and oxides of nitrogen, occur in a numberof environments, where most primarily are responsible for the presenceof disagreeable odors, irritating or toxic gases. Such environmentsinclude landfills, petroleum storage areas, oil and gas refineries,water treatment facilities, sewage treatment facilities, hospitalmorgues, animal rooms, confined livestock operations, swimming pools,and pulp and paper production sites, among others.

There are a wide swath of industries that produce hydrogen sulfide gas.The U.S. Environmental Protection Agency (EPA) is considering broadlyregulating hydrogen sulfide which has been increasingly linked to avariety of health problems for people living or working near petroleum,confined livestock, paper and landfill operations (Wall Street JournalDec. 11, 2007). While it has long been recognized that highconcentrations of hydrogen sulfide are deadly, there is growing evidenceto suggest that hydrogen sulfide may have health effects at low levels.Recent research shows that prolonged exposure to relatively low levelsmay effect memory, coordination, eyes and breathing. With the recentnational housing boom and series of devastating gulf-coast hurricanes,the number of construction and demolition debris sites has risendramatically. This has caused the levels of hydrogen sulfide to alsorise because gypsum, the main ingredient of wallboard, decomposes toproduce hydrogen sulfide as a by-product.

Under current federal rules, companies that produce more than 10,000pounds of hydrogen sulfide must have a plan to avert and respond toaccidental releases of the gas. However, the rules do not generallycover prolonged low-level emissions and contact with people living nearhydrogen sulfide sources.

A U.S. multi-state surveillance program found that 637 hydrogensulfide-related incidents occurred from 1993-2001, resulting in 63public evacuations and injuring 185 people, according to a 2004 JournalArticle written by Federal Health Investigators and others.

More than a dozen states have moved to regulate hydrogen sulfide atlower levels, in the absence of federal rules from the EPA. For example,in 2007, the Department of Environmental Protection for the State ofMassachusetts discussed a policy directed to solid waste managementregulations for the control of odorous gas at Massachusetts landfills.Other states are proposing benchmark standards for interpretingmonitoring data. For example, the Maine Center for Disease Control(ME-CDC) established ambient air guidelines for hydrogen sulfide. Theseguidelines apply to the general public. The Occupational Health andSafety Administration sets exposure standards for site workers. TheME-CDC's ambient air guidelines of 30 parts per billion (ppb) for acute(short term, 30 minute) exposure and 1 ppb for chronic (long-term,greater than 1 year) exposure are not regulatory standards.

While the oil and gas industries and agricultural operations arebelieved to be some of the largest producers of hydrogen sulfide,construction and demolition dumps are emerging as major areas ofconcern. Reports produced by the Federal Agency for Toxic Substances andDisease Registry indicate that hundreds of people living nearconstruction and demolition debris dumps in Ohio and Florida likely havefallen ill in the past decade after being exposed to hydrogen sulfidefor days and weeks.

Different methods can be used to check for hydrogen sulfide and areselected based on site-specific needs. For example, hydrogen sulfide canbe detected and measured with portable or stationary continuous airmonitors. Air sampling and subsequent laboratory analysis can also beconducted.

Hydrogen sulfide and other landfill gases can be controlled byinstalling an active gas management system that pulls out and burns thelandfill gas. Also, hydrogen sulfide emissions can be reduced byapplying certain cover materials such as soil amended with lime and fineconcrete.

Hydrogen sulfide (H₂S) is a colorless, heavier-than-air, toxic gashaving the characteristic odor of rotten eggs. It occurs both naturallyand from industrial processes. Natural sources include crude oil,natural gas, salt marshes, sulfur springs and swamps. Industrial sourcesinclude manure handling operations, oil refineries, pulp and papermills, wastewater treatment plants and solid waste landfills.Controlling emissions of this gas has long been considered desirable.More recently, protecting electronic apparatus from the corrosive fumesof these compounds has become increasingly important. H₂S is alsoflammable.

Chlorine (Cl₂) is a greenish-yellow dense gas with a suffocating odor.The compound is used for bleaching fabrics, purifying water, treatingiron, and other uses. Control of this powerful irritant is mostdesirable for the well-being of those who work with it or are otherwiseexposed to it. At lower levels, in combination with moisture, chlorinehas a corrosive effect on electronic circuitry, stainless steel and thelike. Accordingly, protecting electronic apparatus from the corrosivefumes of chlorine and chlorine by-products is desirable.

Sulfur dioxide (SO₂) is a colorless gas. It can be oxidized to sulfurtrioxide, which in the presence of water vapour is readily transformedto sulphuric acid mist. Health effects caused by exposure to high levelsof SO₂ include breathing problems, respiratory illness, changes in lungdefences, and worsening respiratory and cardiovascular disease. Peoplewith asthma, chronic lung or heart disease are the most sensitive. SO₂also damages trees and crops. SO₂, along with nitrogen oxides, are themain precursors of acid rain. This contributes to the acidification oflakes and streams, accelerated corrosion of buildings and reducedvisibility.

Oxides of nitrogen, including nitrogen dioxide (NO₂) nitric oxide (NO),and nitrous oxide (N₂O), are compounds with differing characteristicsand levels of danger to humans, with nitrous oxide being the leastirritating oxide. Nitrogen dioxide, however, is a deadly poison. Controlof pollution resulting from any of these oxides is desirable ornecessary, depending on the oxide.

Attempts have been made to provide a solid filtration media for removingthe undesirable compounds described above. Desired features of suchmedia are a high total adsorption capacity for the targeted compound,high efficiency in removing the compound from an air or gas stream, anda low ignition temperature (non-flammability). For example, U.S. Pat.No. 4,855,276 describes a solid oxidizing system in pellet form composedof carbon, alumina, and other binders suitably impregnated withchemicals (such as sodium bicarbonate) to enhance the capacity forremoval of odorous gases. This pellet provides air purification and odorcontrol by both adsorbing and adsorbing odors, and then destroying thecollected odors by the pellet's controlled oxidizing action.

Activated carbon will physically adsorb considerable quantities ofhydrogen sulfide. See, for example, U.S. Pat. No. 2,967,587. See alsoFrench Patent No. 1,443,080, which describes adsorption of hydrogensulfide directly by activated carbon, which is then regenerated by hotinert gas or superheated steam.

Better removal of sulfur compounds can be accomplished by the catalysisof the oxidation of hydrogen sulfide to sulfur, based on the ability ofcarbon to oxidize hydrogen sulfide to elemental sulfur in the presenceof oxygen. Additionally, it has been found that potassium sulfate canconvert hydrogen sulfide into elemental sulfur. Both the above reactionsare advantages because they allow for greater storage of contaminants inthe solid filtration media because the contaminants are broken down intosmaller molecules and consequently take up less space within the solidfiltration media. Ammonia may be added to an influent gas stream ofhydrogen sulfide and oxygen to provide catalysis. Silicate-impregnatedactivated carbon is also effective. The residual adsorbate, however, maynot be removed by extraction with alkaline solutions. See South AfricanPatent No. 70/4611. Treatment with a 1% solution of NaOH restores theadsorption capacity of activated carbons used for adsorption removal ofhydrogen sulfide gas. Boki, Shikoku Igaku Zasshi, 30(c), 121-8 (1974)(Chemical Abstracts, Vol. 81).

See also, for example, French Patent No. 1,388,453, which describesactivated carbon granules impregnated with 1% iodine (I₂) for this use.South African Patent No. 70/4611 discloses the use ofsilicate-impregnated activated carbon. Swinarski et al, Chem. Stosowana,Ser. A 9 (3), 287-94 (1965), (Chemical Abstracts, Vol. 64, 1379c),describe the use of activated carbon treated with potassium salts,including potassium hydroxide (KOH) for hydrogen sulfide adsorption.Activated carbon has also been impregnated with a solution of sodiumhydroxide (NaOH) and potassium iodide (KI).

Although not confirmed, U.S. Pat. No. 4,072,479 suggests that hydrogensulfide is oxidized to elemental sulfur in the presence of activatedcarbon, and that the presence of moisture on the activated carbon issignificant. Another method for removing sulfur and other compounds fromgas streams utilizes a product known as Purakol K (Lindair, Ljusne,Sweden). This product contains carbon impregnated with NaOH and KI.

Other uses of impregnated carbon include removing water from air(desiccation), see, for example, Soviet Union Patent No. 1,219,122(activated carbon combined with aluminum oxide; a binder, calciumhydroxide; and lithium bromide); and the removal of acidic contaminantsfrom gas streams, see, for example, U.S. Pat. No. 4,215,096 (activatedcarbon impregnated with sodium hydroxide and moisture, for the removalof chlorine from gas streams) and U.S. Pat. No. 4,273,751 (activatedcarbon impregnated with sodium hydroxide and moisture, for the removalof sulfur oxide gases and vapors from gas streams).

Japanese Patent No. 61-178809 teaches water purification by treatmentwith activated carbon loaded with metallic copper or copper salts.Several patents teach alumina and carbon adsorbents, including U.S. Pat.No. 3,360,134 (alumina hydrate contacted with a carbonaceous solution;used as a decolorizing agent, a reviving agent for precious metalelectroplating bath for the removal of constituents from cigarettesmoke, and as an adsorbent in pressure or gravity flow percolationbeds); U.S. Pat. No. 4,449,208 (powdered carbon, dense alumina, and abinder, for increasing heat capacity of the adsorbent to enhance theoperation of adiabatic pressure swing adsorption processes by decreasingthe cyclic temperature change in the adsorbent bed during each cycle ofthe process); U.S. Pat. No. 3,819,532 (ground graphite and finelydivided alumina adsorbent, for removing aromatics, heterocyclics, sulfurcompounds, and colored materials from lubricating oils); and U.S. Pat.No. 3,842,014 (ground graphite and alumina binder, for adsorbingparaffin). Such art generally teaches a substrate consisting primarilyof activated carbon with a relatively small amount of alumina.

Finally, U.S. Pat. No. 7,101,417 teaches a method of reducing aconcentration of hydrogen sulfide present in a gaseous dischargecomprising contacting the gaseous discharge with an activatedcarbon/metal oxide filter element constructed and arranged to exhibit astructural failure when saturated with sulfur, thereby producing aproduct stream having a reduced hydrogen sulfide concentration, andremoving the product stream from the activated carbon/metal oxide filterelement. U.S. Pat. No. 7,101,417 indicates that one important advantageof the media claimed is that the media is arranged and constructed toexhibit structural failure when saturated with a odorous compound suchas hydrogen sulfide.

None of the methods available thus far have effectively addressedneutralization of large quantities of gases while maintaining structuralintegrity. Accordingly, there remains a need for a composition having anenhanced capacity for toxic or harmful gases, such as hydrogen sulfideremoval. Furthermore, there remains a need for a toxic or harmful gasesremoval composition that can operate effectively and not present healthproblems to those who use or install the composition.

SUMMARY OF THE INVENTION

Compositions and methods are provided herein for the capture andneutralization of large quantities of toxic or harmful compounds in anair-stream. Typically, the toxic or harmful compounds are acid gases. Inparticular, the compositions and methods described herein effectivelyabsorb and adsorb compounds such as, but not limited to, hydrogensulfide, chlorine, nitrogen dioxide, fluorides and sulfur dioxide.

The compositions described herein are dry-scrubbing media containingactivated alumina and magnesium oxide. The dry scrubbing media mayoptionally include powdered activated carbon. Additionally, the dryscrubbing media may be impregnated with other substances, such as sodiumhydroxide or potassium hydroxide.

The dry-scrubbing media provided herein exhibits an enhanced capacity toadsorb undesired compounds at a higher efficiency than commerciallyavailable media. In addition, the incorporation of magnesium oxideimparts increase storage capacity for contaminants because the magnesiumoxide converts hydrogen sulfide into elemental sulfur, which takes upless space than the original contaminant on the solid filtration media.Further, use of powdered activated carbon reduces production costs. Inaddition, the use of sodium hydroxide or potassium hydroxide as animpregnate facilitates chemical absorption of chlorine to thedry-scrubbing media.

In contrast to media known in the prior art, the dry-scrubbing media ofthe instant application is not arranged or constructed to exhibitstructural failure when saturated with an odorous compound, such ashydrogen sulfide. For example, applicants have overcome problems withdisintegration of prior art media saturated with an odorous compoundthat consequently leads to a reduction in filtration efficiency andoverall contaminant removal. This occurs because the leading edge of theprior art media disintegrates, clogging or reducing the filtrationprocess.

Granular carbon is used in conventional filtration system and issignificantly more expensive than powdered carbon. Powdered carbon is aby-product of granular carbon production. However, powdered carbon istoo fine and dusty for use in solid filter beds.

The composition provided herein may be used to treat, prevent, or filterthe release of toxic compounds from at least the following locations:landfills, petroleum storage areas, refineries, water treatment systems,sewage treatment facilities, hospital morgues, animal rooms, swimmingpools, and pulp and paper production sites.

The unexpected and surprising ability of the composition to absorb oradsorb large quantities of harmful or toxic gaseous compounds, such ashydrogen sulfide, addresses a long-felt, unfulfilled need in the art andprovides an important health benefit for animals and the environment.

Therefore it is an object of the present invention to provide anefficient, inexpensive method for preventing or reducing the release ofharmful or toxic gaseous compounds.

Another objective of the present invention is to provide an efficient,inexpensive method for filtering harmful, toxic or odorous compoundsfrom an air or gas stream.

Yet another object of the present invention is to provide an adsorbentcomposition that combines and catalyzes or exceeds the individualadsorptive, deodorizing or filtering properties of the individualcomponents of the composition.

These and other objects, features and advantages of the presentinvention will become apparent after a review of the following detaileddescription of the disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Dry-scrubbing media compositions and methods of production and use areprovided herein. The dry-scrubbing media provides air purification andodor control by absorbing and adsorbing odors and then destroying thecollected odors through chemical interaction on the surface of thedry-scrubbing media.

Dry-Scrubbing Media Compositions

The dry-scrubbing media composition described herein contains activatedalumina and magnesium oxide. In one embodiment, the dry-scrubbing mediafurther includes powdered activated carbon. In another embodiment, thedry-scrubbing media is impregnated with sodium hydroxide or potassiumhydroxide.

The dry-scrubbing media compositions provided herein have an enhancedcapacity for the adsorption of certain undesired compounds at a higherefficiency than currently available media. In addition, thedry-scrubbing media compositions described herein enjoy increasedcapacity for the removal of contaminants due to the conversion ofhydrogen sulfide to elemental sulfur via magnesium oxide. It has beenunexpectedly discovered that the use of magnesium oxide in thedry-scrubbing media greatly increases hydrogen sulfide removal capacity.

The addition of powdered activated carbon reduces production costsbecause powdered activated carbon is less expensive than granularcarbon. Powdered carbon is a by-product of granular carbon production.Powdered carbon is not normally used in solid filtration systems due toits fine and dusty characteristics.

The filtration media art has for years generally pursued carbon andalumina adsorbent media as alternative media.

An activated alumina preferably employed in the present composition ismanufactured by Engelhard Corporation, Iselin, N.J. or BASF Corporation,Florham Park, N.J. However, other acceptable, or suitable, activatedalumina may be used. Suitable activated alumina is characterized asworkable, or dehydrated with a loss on ignition (LOI) characteristic ofpreferably less than or equal to 20, and most preferably, an LOI of lessthan or equal to 10.

Powdered activated carbon may be used instead of granular activatedcarbon, and is preferred over granular activated carbon. Carbon blackalso may be used. Activated carbon, powdered carbon and carbon black arecollectively referred to herein as “high surface area carbon.” The sizerange of the powder is largely a matter of choice, although whenproducing pellets of dry-scrubbing media, some parameters are necessaryfor insuring that uniform pellets are achieved during rolling. In oneembodiment, carbon is sized for passing 85% through a −325 mesh screen.In another embodiment, the carbon is sized for passing through a −50mesh screen.

It has been noted that the rate of adsorption can vary upon the surfacearea of the activated carbon used. Accordingly, it is important toemploy activated carbons having high surface areas, preferably between500 and 2000 m²/g surface area, and most preferably between 1000-1200m²/g. An activated carbon preferably employed in the present compositionis manufactured by NORIT Americas, Inc., Marshall, Tex. However, it willbe understood by those skilled in the art that other acceptableactivated carbons may be used.

In embodiments that contain powdered activated carbon, it is preferredthat the proportion of high surface area carbon be about 30% or more.

The magnesium oxide preferably employed in the present composition isavailable from magnesium specialists, Martin-Marietta, Baltimore, Md.Other acceptable sources or manufacturers of magnesium oxide may beused.

The impregnates used may be hydroxides of Group 1A metals. Inparticular, the impregnate is sodium hydroxide or potassium hydroxide.While it is not clear how the impregnate functions in the dry-scrubbingmedia, it is believed that the impregnate reacts directly with theadsorbed undesired compound.

While not wishing to be bound by the following theory, it is believedthat the dry-scrubbing media compositions provided herein utilize achemisorptive process that removes hydrogen sulfide by means ofabsorption, adsorption and chemical reaction. Hydrogen sulfide istrapped within the dry-scrubbing media where an irreversible chemicalreaction takes place, changing the gas into solids trapped in thedry-scrubbing media. The chemical reaction occurs on the surface of thedry-scrubbing media. Additionally, the dry-scrubbing media may be housedin an apparatus designed to allow a reaction front to move down adry-scrubbing media-packed column as release of a odorous compoundproceeds. This feature allows for partial releases to consume only aproportional amount of the media. Accordingly, the dry-scrubbing mediacomposition provides substantial cost-savings in terms of usage andreplacement materials. One advantage of the instant media over the priorart is that the dry-scrubbing media described herein is not arranged orconstructed to exhibit structural failure when saturated with an odorouscompound.

In one embodiment, an apparatus housing the dry-scrubbing media is areaction chamber, filter bed or column. In another embodiment thedry-scrubbing media is prepared in pellet form. The pellets may beloaded into the reaction chamber, filter bed or column for use withinthe apparatus.

In an alternative embodiment, the dry-scrubbing media is prepared viaextrusion to form a matrix or honeycomb structure containing multiplechannels that pass through the length of the extruded dry-scrubbingmedia. One advantage of dry-scrubbing media prepared via extrusion isthat the matrix or honeycomb structure produced provides a significantsurface area for chemical reactions to take place between contaminants,such as hydrogen sulfide, and the dry-scrubbing media as the air-streampasses through the matrix structure. The dry-scrubbing media'schemisorptive process removes hydrogen sulfide by means of adsorption,absorption and chemical reaction.

In either embodiment, a harmful or toxic gas, such as hydrogen sulfide,is trapped within the dry-scrubbing media pellets or matrix where anirreversible chemical reaction changes the gas into a harmless solid.The chemical reaction occurs on the surface of the dry-scrubbing mediapellets or matrix throughout the volume of the pellets or matrix. In theevent of exposure to a gas, such as hydrogen sulfide, a reaction frontmoves down the dry-scrubbing media-packed column or matrix as the gasrelease proceeds. This allows for partial releases to consume only aproportional amount of media.

In contrast to wet-scrubbing systems currently available, thedry-scrubbing media provided herein requires little maintenance to yieldhigh reliability. It is noted that the dry scrubbing media's efficiencyis not directly dependent on how well the system is maintained.

Advantageously, the dry-scrubbing media, quite unlike wet-scrubbingmedia, is not highly corrosive, toxic, hazardous and does not have alimited shelf-life.

Furthermore, it is also noted that currently available wet-scrubbingsystems can be converted or retrofitted with the components of thedry-scrubbing media as disclosed herein, thereby providing enhancedcapacity to capture or neutralize toxic gases such as hydrogen sulfide.

Other benefits of the compositions described herein include that thedry-scrubbing media is landfill disposable and does not requirespecialist disposal and costs associated therewith. The media is alsonon-toxic and non-hazardous before and after reaction or usage. Thedry-scrubbing media, while having enhanced hydrogen sulfide removalcapacity over media known and currently used in the art, also allowsretrofitting of wet-scrubbing systems with the dry-scrubbing mediaresulting in enhanced hydrogen sulfide removal.

Wet scrubbing of effluent streams involves contacting the effluent gasfrom a specific process with a scrubbing liquid to cause undesiredeffluent stream components to be absorbed by the liquid, or to reactwith the liquid (e.g., a caustic solution for contacting with an acidgas effluent) to effect the removal of the undesired components from thegas phase. Often the scrubbing liquid includes an oxidizing agent suchas potassium permanganate, a regulated substance, or sodiumhypochlorite, which leads to unwanted precipitation reactions. Further,the wet scrubbing system requires the consumption of significant amountsof the oxidizing agents and leads to a contaminated aqueous wastestream.

In contrast, a dry-scrubbing media involves contacting an effluent gasstream with a solid material which functions to chemisorb or react withthe undesired components to effect their removal. The dry-scrubbingmedia described herein concentrates and fully contains hazardouscontaminants, is passive in operation, has no moving parts and works ondemand, making it a safe and preferable mode of filtration andpurification.

In one embodiment the dry-scrubbing media provides an adsorbentcomposition as a dry feed mix containing from about 40% to about 99%activated alumina by weight and from about 1% to about 60% magnesiumoxide by weight of the composition.

In another embodiment the dry-scrubbing media provides an adsorbentcomposition as a dry feed mix containing from about 40% to about 60%activated alumina by weight and from about 40% to about 60% magnesiumoxide by weight of the composition.

In one embodiment the dry-scrubbing media provides an adsorbentcomposition as a dry feed mix containing from about 50% to about 99%activated alumina by weight and from about 1% to about 50% magnesiumoxide by weight of the composition.

It is believed that the alumina in the composition results in a moreopen pore structure containing “macropores.” Such a structure is lesslikely to be clogged by the adsorbed compounds than activated carbonalone. This may explain why the composition provided herein has agreater adsorption capacity and efficiency than unimpregnated as well asimpregnated activated carbons. Furthermore, the activated aluminasupports the carbon, provides hardness even at very high surface areas,and increases the ignition temperature of the composition.

In another embodiment, the dry feed mix may optionally include activatedcarbon. In this instance, the dry feed mix contains about 20%-30%activated alumina, about 20%-30% magnesium oxide and about 40-60%activated carbon, all by weight of the composition.

In a further embodiment, the dry feed mix contains about 30% activatedalumina, about 20% magnesium oxide and about 50% activated carbon, allby weight of the composition.

In another embodiment the dry feed mix contains about 40% to about 60%activated alumina and about 40% to about 60% magnesium oxide by weightof the composition can be optionally sprayed with a liquid or animpregnate. In one embodiment the liquid sprayed onto the dry mix iswater. Generally, the amount of liquid applied to the dry feed mix isabout 5% to about 50%. In another embodiment, the dry feed mix issprayed with an impregnate, such as a hydroxide. Generally, a 5% toabout 20% solution of a hydroxide solution, for example, sodiumhydroxide or potassium hydroxide is applied or sprayed onto the dry mix.

In another embodiment, an adsorbent composition is provided as adry-scrubbing media in final form “ready for use”. In one embodiment,the dry-scrubbing media may be directly applied to a column, filter bed,reaction chamber or an apparatus to create a purification or filtrationapparatus. Generally, under such conditions, the adsorbent compositioncontains about 40% activated alumina, about 40% magnesium oxide andabout 20% liquid, sprayed or applied during the dry-rolling or tumblingprocess so as to form nodules. In one embodiment the liquid appliedduring the manufacturing process is water.

In another embodiment wherein the dry-scrubbing media includes activatedcarbon, the dry-scrubbing media contains about 15-25% activated alumina,about 15-25% magnesium oxide, about 15-20% water and about 30%-55%activated carbon.

In a further embodiment the dry-scrubbing media contains activatedalumina and magnesium oxide and can optionally include an impregnatesuch as a hydroxide. Typically, about 1% to about 10% of thedry-scrubbing media by weight includes a hydroxide.

As mentioned above, the dry-scrubbing media can be prepared ormanufactured by extrusion to form a solid structure. Extrusion is amanufacturing process used to create long objects of a fixedcross-sectional profile. A material, or mixture, is pushed and/or drawnthrough a die of the desired profile shape. The die may be of differentshapes and diameters. Extrusion of the dry-scrubbing media providedherein can be performed by squeezing a mixture of activated alumina andmagnesium oxide through a die using either mechanical or hydraulicmeans. In one embodiment, the dry-scrubbing media is prepared viaextrusion to form a matrix or honeycomb structure or shape, containingmultiple channels passing through the length of the extrudeddry-scrubbing media. The honeycomb has a matrix of porous walls,composed of the dry-scrubbing media, forming a multiplicity of cellsextending from one end (proximal) to another end (distal) of thehoneycomb. One advantage of dry-scrubbing media prepared via extrusionis that the matrix or honeycomb provides a greater surface area forchemical reactions to take place between contaminants in an air-streamand the dry-scrubbing media. In one embodiment, the dry-scrubbing mediaproduced under extrusion is composed of activated alumina and magnesiumoxide. In another embodiment, the extruded dry-scrubbing media mayfurther include activated carbon. In another embodiment, thedry-scrubbing media produced by extrusion to form a matrix or honeycombmay further include impregnates, such as an hydroxide. Impregnates canbe applied to the dry-scrubbing media before, during, or afterextrusion. It is to be understood that the process of extrusion is wellknown in the art, and that any means of extrusion including but notlimited to, cold extrusion and hot extrusion, are encompassed herein.Furthermore, additives such as colorants and UV inhibitors (in eitherliquid or pellet form) are often used and can be mixed with theactivated alumina and magnesium oxide mixture prior to extrusion.Plasticity and shape retention of extruded materials can be varied orimproved through the use of binders. The binder is not particularlylimited and there may be used any of various types of binders which isused when a molded product is made by extrusion molding or injectionmolding. More specifically, there are exemplified various types ofalcohols, celluloses such as methyl cellulose, ethyl cellulose etc.,starches, vinyl resins, various waxes, thermoplastic polyolefins such aspolyethylene, polypropylene etc., polyacetate vinyl compounds etc. Inone embodiment, binders include but are not limited to, starchadhesives, organic binders, clay, and feldspar.

While not wishing to be bound by the following theory it is believedthat the honeycomb or matrix structure produced by extrusion allows forthe formation of pores or channels in the solid structure resulting inan increase in total surface area available for chemical interactionwith contaminants.

In another embodiment, a system for forming powderized or pelletizeddry-scrubbing media products of higher density, with less dust, bettergranularity and better flow characteristics than currently availablemedia is provided. A system is provided for pelletizing thedry-scrubbing media, and thereafter subjecting the pellets to a millingprocess to obtain a powdered form. During pelletizing, steam can beadded. The resulting powder is denser, more granular and has better freeflow properties than the pre-pelletized material. The powderizeddry-scrubbing media can be used in a reaction chamber or column.

It is to be understood that one of ordinary skill in the art may developor modify the dry-scrubbing media described herein in addition to thepellitization and extrusion methods discussed above. Indeed, it isenvisaged that the dry-scrubbing media may have any suitable size, shapeand conformation appropriate to the end use application and the removalof contaminants, such as hydrogen sulfide from gas or air-streams. Thedry-scrubbing media may further include active ingredients and inactiveingredients, and may be in a finely divided form, e.g., beads, spheres,rings, toroidal shapes, irregular shapes, rods, cylinders, flakes,films, cubes, polygonal geometric shapes, sheets, coils, helices,meshes, granules, pellets, powders, particulates, extrudates, honeycombmatrix, composites (of the dry-scrubbing media with other components),or crushed forms of the foregoing conformations.

In one embodiment, the dry-scrubbing media is used for hydrogen sulfidegas removal and is at least 10% minimum by weight. For example, 100 lbsof dry-scrubbing media removes at least 10 lbs of hydrogen sulfide. In afurther embodiment, the dry-scrubbing media for hydrogen sulfide gasremoval is about 20% minimum by weight. For example, 100 lbs ofdry-scrubbing media removes at about 20 lbs of hydrogen sulfide. Inanother embodiment, the dry-scrubbing media for hydrogen sulfide removalis about 30% minimum by weight. For example, 100 lbs of dry-scrubbingmedia removes at about 30 lbs of hydrogen sulfide. In yet anotherembodiment, the dry-scrubbing media for hydrogen sulfide removal is atleast 50% minimum by weight. For example, 100 lbs of dry-scrubbing mediaremoves at least 50 lbs of hydrogen sulfide.

The adsorbent composition generally described as a dry-scrubbing mediaincludes activated alumina and magnesium oxide. The dry-scrubbing mediamay further include water and activated carbon. It is believed that themagnesium oxide may synergistically assist the chemical reactionsinvolving compounds adsorbed by the composition.

The composition may preferably include an impregnate operative to causeinactivation of an undesirable substance in a air-stream passing over orthrough the composition. The impregnate preferably is a hydroxide of aGroup 1A metal. For example, activated alumina and magnesium oxide maybe impregnated with a hydroxide, such as potassium hydroxide or sodiumhydroxide.

Process of Making Dry-Scrubbing Media Compositions

A process for making a dry-scrubbing media composition is describedherein. In one embodiment, a mixture of activated alumina, magnesiumoxide and a liquid is formed into at least one cohesive unit, and thecohesive unit cured at an elevated temperature, preferably 100-225° F.for at least one hour. Preferably, a dry feed mix is made of theactivated alumina and magnesium oxide, and the dry feed mix is tumbledor rolled while being sprayed with a liquid, for example water. The dryfeed mix may further include powdered activated carbon.

Heating the impregnating solution prior to rolling the pellets in atumble mill appears to allow the pellets to begin curing immediately,yielding better physical characteristics than an impregnating solutionapplied at room temperature. This can be achieved using a solutiontemperature between about room temperature and the boiling point of thesolution. The preferred solution temperature is about 50° F. to about200° F.

The combination of activated alumina, magnesium oxide and water may becarried out in any manner that effectively produces an adsorbent formedof a dry mix containing about 20% to about 80% by weight of activatedalumina, and about 1% to about 60% by weight of magnesium oxide.Typically, 5% to 30% water should be contained by weight of the curedadsorbent product. In one embodiment, the amount of alumina in the drymix is from about 40% to about 60% by weight. In one embodiment, theamount of magnesium oxide is from about 40% to about 60% by weight. In apreferred embodiment, the final product contains from about 5% to about20% by weight of water.

The amount of moisture present in the composition will depend on severalfactors, related primarily to the characteristics of the activatedalumina being treated. The desired moisture content of the compositionis readily obtained by spraying the dry mix ingredients while they rollon the mixer, in accordance with the method of U.S. Pat. No. 3,226,332.

The combination of activated carbon powder with activated alumina andmagnesium oxide similarly may be carried out in any manner thateffectively combines a dry mix containing about 1% to about 50% byweight of magnesium oxide; about 10% to about 40% by weight of activatedcarbon powder; and about 40% to about 60% by weight of activatedalumina.

In another embodiment the dry feed mix contains about 25% by weightactivated alumina, about 25% by weight magnesium oxide and about 50% byweight activated carbon powder.

The combination of activated carbon powder with activated alumina,magnesium oxide and water similarly may be carried out in any mannerwhich effectively combines about 15% to about 25% by weight of magnesiumoxide; about 30% to about 55% by weight of activated carbon powder,about 15% to about 25% by weight of activated alumina; and about 15% toabout 20% water.

Impregnation of either of the above combinations may be carried out inany manner which effectively produces an adsorbent of about 0.1% toabout 15% by weight of impregnate formed by using a solution of about0.3% to about 40% impregnate. Impregnation may be carried out simply bysoaking the combinations in one volume of impregnate solution. The timerequired to produce the desired impregnation level is dependent upon theimpregnate employed, and will only be as much time as is needed for theimpregnate to penetrate the combinations. Additionally, the impregnatesolution may be heated prior to use, for example during preparation of adry-mix or during a tumbling/rolling process.

In one embodiment, impregnation with a hydroxide may be carried out byusing a solution of about 3% to about 20% sodium hydroxide or potassiumhydroxide. The resulting pellet should contain from about 1% to about10% by weight hydroxide. Impregnation with other suitable impregnatesalso may be carried out in any manner that effectively produces anadsorbent of about 1% to about 10% by weight of impregnate, formed byusing a solution of up to about 40% impregnate.

Other methods of impregnating the dry-scrubbing media will suggestthemselves as equally appropriate and these are included within thescope of the present invention. For example, the impregnate solution maybe passed through the media rather than being used in a static immersiontreatment. However, it has been found that a preferred method ofimpregnation is “spray addition” in which an impregnate solution issprayed onto the dry combination being tumbled in a mixer. This methodof impregnation has been described in U.S. Pat. No. 3,226,332.

Additionally, as mentioned above, the dry-scrubbing media may be formedby extrusion to form a matrix or honeycomb structure. The formation ofchannels and pores in a matrix creates a large surface area for chemicalreactions to occur between contaminants in an air-stream and the surfaceof the dry-scrubbing media.

Pellets of dry-scrubbing media can be manufactured using standardequipment known in the preparation of pelletized products. Severalmanufacturers are known to one of ordinary skill in the art and suchequipment is used in a wide array of industries. The advantagesassociated with a pelletized material include control of dust. Thecontrol of dust is important in the present method because an air-streammust pass through the dry-scrubbing media. If the dry-scrubbing mediabecomes clogged due to dust, this may impact the level or efficacy ofchemical reactions occurring between contaminants and the dry-scrubbingmedia.

To process pellets, activated alumina and magnesium oxide can be fed ata constant rate onto a rotating disk that is oriented at an adjustableangle above horizontal. As the disk rotates, a liquid binder is sprayedonto the surface of the powder, and the combined materials are caused totumble down the face of the disk, thus producing rolled pellets. Thepellets roll from the lower end of the disk as new powder and binder areadded at the upper end of the disk. In preferred aspects, the disk is agranulating pan, and is provided with at least one scraper, and istilted at an angle of from 10°-80° from the vertical. More preferably,the method further includes sizing the pellets by passing the pelletsthrough a sieve.

Methods of Use

A method of removing impurities from air or gas stream is provided. Inaccordance with the method, the dry-scrubbing media compositiondescribed above is contacted with an air-stream containing impurities tobe removed. The dry-scrubbing media is particularly useful for theremoval of hydrogen sulfide from an air-stream. At some levels ofremoval efficiency, pellets embodying the composition will last over 50%longer than activated carbon impregnated with sodium hydroxide, and willprovide better removal efficiency. The dry-scrubbing media describedherein is also useful for removing chlorine gas and hydrocarbons fromair-streams.

The dry-scrubbing media compositions may be particularly useful for thereduction or prevention of the release of toxic gaseous compounds fromat least the following locations: landfills, water disinfection systems,municipal waste treatment facilities, petrochemical refining plants,swimming pools, hospitals, hotel facilities, petroleum storage areas,refineries, water treatment systems, sewage treatment facilities,hospital morgues, animal rooms, pulp and paper production sites, and thelike.

The concentration of these undesirable compounds in the air-stream isnot considered critical to the process, and concentrations resulting inlevels as low as less than 1 part per billion (ppb) at discharge of thecompounds passing through the dry-scrubbing media can be achieved.

The physical and chemical makeup of the air-stream from which it isdesired to remove undesirable compositions is not critical. It may beimportant that oxidizing conditions prevail but it is not known to whatextent oxidation may affect the purification achieved. Typically, theundesired compositions will be removed from air, especially from airadmixed with effluent gas streams. The oxidizing conditions that may beimportant are generally that oxygen be present in the air-stream beingtreated, at least in small amounts. If oxygen is totally absent orpresent in insufficient amounts, oxygen may be independently introducedinto the air-stream being treated. A number of factors affect the amountof oxygen that may be required for maximum adsorption in accordance withthe present method, including the concentration and absolute amount ofcompounds being adsorbed from the air-stream being treated.

With respect to the amount of compound adsorbed, it is recognized thatthe following factors affect the process: the basic degree of attractionof activated alumina and magnesium oxide for the compound; the porestructure and size of the activated alumina, the specific surface areaof the activated alumina; and the surface characteristics of theactivated alumina. In embodiments containing dry-scrubbing media andactivated carbon, specific surface area and surface characteristics ofactivated carbon can effect the amount of compound or contaminantabsorbed.

The impregnation treatment of the activated starting material inaccordance with the present method has not been found to be criticalwith respect to the particular sequence in which the dry scrubbing mediais impregnated with moisture and impregnates.

The dry-scrubbing media composition is appropriately used alone incolumns for the removal of undesirable compounds. It is alsoappropriate, however, to use the dry-scrubbing media in conjunction withcolumns containing other adsorbents. Such combination is especiallyappropriate when high levels of contaminants or hydrocarbons are presentin the air-stream. Any such column may be placed either upstream (beforethe dry-scrubbing media with respect to the effluent gas or air streambeing treated) or downstream.

It has also been found that flow rates of the gas stream being treatedwith the dry-scrubbing media do not affect the breakthrough capacitiesof the dry-scrubbing media. However, a preferred flow rate is between 10and 750 ft/min, and most preferably is between 50 and 150 ft/min.

The following examples will serve better to illustrate the compositionand the treatment methods and the adsorption capacity produced thereby.Reference is made to a tumble mill in the following examples. Suchreference is to a small scale rolling disc used in a laboratory setting.The disc is 14″ in diameter with a depth of 4″. The disc is angled at30° from the vertical, and operated at a speed of 20 rpm. By comparison,a full scale production disc is typically 6 feet in diameter with adepth of 4″, and is operated at the same angle and the same speed. Thelaboratory conditions yield pellets that are approximately the same sizeas the full scale disc, but not as strong, because the periphery of thedisc moves at a slower speed. Thus, the pellets do not experience thesame amount of force during rolling. Therefore, it is expected thatpellets formed on a full scale disc using the same starting materials asdescribed in the following examples would be stronger, and would performbetter than as indicated in the examples. It should be noted that thecontinuous flow systems described in several of the following exampleswill be operated in a relative humidity of 40-50%.

The present invention is further illustrated by the following examples,which are not to be construed in any way as imposing limitations uponthe scope thereof. On the contrary, it is to be clearly understood thatresort may be had to various other embodiments, modifications, andequivalents thereof, which, after reading the description herein, maysuggest themselves to those skilled in the art without departing fromthe spirit of the present invention.

Example 1

A dry-feed mix is prepared by combining, by weight, about 15% to about35% activated alumina, about 5% to about 50% magnesium oxide and about20% to about 60% activated carbon.

Example 2

A dry-scrubbing media is prepared by combining, by weight, 40% activatedalumina, 40% magnesium oxide and sprayed with 20% water at 200° F. whilethe dry feed mix is tumbled in a tumble mill. The resulting pellets arethen dried at 135-140° F. in air, relative humidity at about 35%, untilthe pellets contain about 10% by weight moisture.

Example 3

A dry-scrubbing media is prepared by combining, by weight, 30% activatedalumina, 20% magnesium oxide, 30% activated carbon powder and 20% water.The mix is sprayed with a 15% sodium hydroxide aqueous solution at 200°F. while the dry feed mix is tumbled in a tumble mill. The resultingpellets are then dried at 135-140° F. in air, relative humidity at about35%, until the pellets contain about 5% to about 10% by weight of sodiumhydroxide.

Example 4

A dry-scrubbing media is prepared by combining, by weight, 25% activatedalumina, 25% magnesium oxide and 50% activated carbon powder. The dryfeed mix is sprayed with a 15% potassium hydroxide aqueous solution at200° F. while the dry feed mix is tumbled in a tumble mill. Theresulting pellets are then dried at 135-140° F. in air, relativehumidity at about 35%, until the pellets contain about 5% to about 10%by weight of potassium hydroxide

While this invention has been described in detail with regard topreferred embodiments thereof, it should be understood that variationsand modifications can be made without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A method for preventing or reducing release of acontaminant from an air stream comprising administering a dry-scrubbingmedia composition comprising 15-25% by weight activated alumina, 15-25%by weight magnesium oxide, 30-55% by weight activated carbon and 15-20%by weight water to an air stream, wherein the dry-scrubbing media iseffective to remove the contaminant from the air stream.
 2. The methodof claim 1, wherein the contaminant is hydrogen sulfide.
 3. The methodof claim 1, wherein the dry-scrubbing media composition is in a form ofa honeycomb structure.
 4. The method of claim 1, wherein thedry-scrubbing media composition further comprises a hydroxide of a GroupIA metal.
 5. The method of claim 4, wherein the hydroxide is sodiumhydroxide or potassium hydroxide.
 6. The method of claim 1, wherein thedry-scrubbing media composition further comprises about 5% to about 10%by weight of sodium hydroxide or potassium hydroxide.
 7. The method ofclaim 6, wherein the dry-scrubbing media composition is in a form of ahoneycomb structure.
 8. The method of claim 1, wherein the air stream isflowing past the dry-scrubbing media composition at a rate of from 10 to750 ft/min.
 9. The method of claim 1, wherein the air stream is flowingpast the dry-scrubbing media composition at a rate of from 50 to 150ft/min.